A major energy transition is underway to establish a sustainable global net-zero CO2 economy. Molecular hydrogen (H2) is an attractive alternative to replace carbon-based fuels in energy-intensive industries and for domestic use, and it attracts public interest as well as industry and government support. However, economic carbon-free H2 production is challenging. Unicellular green algae have evolved over billions of years to tap into the immense energy resource of the sun using photosynthesis. Green algae are highly productive, with a theoretical maximum photon conversion efficiency (PCE) of ~10%. Some species of green algae, like the photosynthetic model organism Chlamydomonas reinhardtii, can produce H2 via an endogenous hydrogenase (HydA), which is directly linked to the photosynthetic electron transport chain. This process is now being optimised for industrial applications by engineering a series of key photosynthetic steps affecting photosynthetic H2 production by increasing light-to-H2 conversion efficiency. This project aims to enhance the light-to-H2 PCE of green algae towards this 10% theoretical maximum by combining these engineered improvements into a single microalga strain using a recently developed sequential scarless CRISPR-Cas9 gene editing strategy. This improved hydrogen production chassis provides the basis for a production platform for other products by exchanging HydA with other redox enzymes to enable the production of higher-value biochemicals and pharmaceuticals.